1. Field
Polishing slurries and particles.
2. Background
Typical integrated circuit (“IC”) manufacturing techniques involve the fabrication of multiple IC chips on a single semiconductor or substrate wafer. In turn, each chip may be made up of millions of electronic devices (e.g., transistors, resistors, capacitors) formed in the silicon substrate. Generally, the function of each device is dictated by the chemical makeup and geography of the substances it contains. Thus, during fabrication, the formation of these devices involves a sequence of operations aimed at adding, shaping and removing various chip substances by having these substances grown, deposited, removed, chemically altered, and polished in selected areas on the wafer. For instance, the surface of a wafer may be polished to assure that the device surfaces are flat or to remove excess material from the surface of the devices prior to the next manufacturing operation. Polishing of wafer surfaces is often referred to as “planarization”.
One technique for planarizing the top surface of semiconductor wafers is to polish the surface using a polishing “slurry” having abrasive particles mixed in a solution or suspension agent in a chemical-mechanical polishing (CMP) process. CMP processes and slurries are used for the polishing of semiconductor wafers, inter-layer dielectric layers, metal layers or lines, thin films, and other components during integrated circuit manufacturing. For instance, CMP is often used for planarizing tungsten interconnects, vias and contacts. CMP slurries typically include abrasive particles such as alumina; silica or ceria, such as oxides of aluminum, silicon or cerium; a ferric salt oxidizer such as ferric nitrate; a suspension agent such as propylene glycol; and deionized water. In CMP, the abrasive particles provide friction while oxidants and/or etchants can be used to cause a chemical reaction at the wafer surface. Slurry additives can also be used to enhance the removal rate, uniformity, selectivity, etc.
In a typical chemical mechanical polishing process, the substrate or wafer is placed face-down on a polishing pad which is attached to a rotatable table. In this way, the material to be polished (e.g., a tungsten or copper film) is placed in direct contact with pad. A carrier can be used to hold the wafer, as well as to apply a downward pressure against the backside of substrate. During the polishing process, pad and table are rotated while a downward force is placed on substrate by carrier. The abrasive and chemically reactive solution or “slurry” is introduced or deposited onto the pad during polishing. The slurry initiates the polishing process by chemically reacting with the material (e.g., a film) being polished. The polishing process is facilitated by the rotational movement of pad relative to wafer as slurry is provided to the wafer/pad interface. Polishing is continued in this manner until a desired amount of the material (e.g., all of the film on the insulator) is removed.
Commercially available CMP equipment and slurries are available for planarization of integrated circuits. Typically, a high-shearing type dispersion machine is used to produce the abrasive particles for a CMP slurry solution. However, current CMP slurries exhibit problems such as separation within the slurry of abrasive and additive particles, displacement of additives due to a shortage of chemical reactions between the abrasive and additive particles, and non-uniform distribution of the abrasive and/or additive particles in the slurry.